Single ply roof guarantees often cover 15-20 years, but the real service life...

https://spark-wiki.win/index.php/What_Should_a_Roof_Survey_Focus_on_for_an_Older_Single_Ply_Membrane%3F

Single ply roof guarantees often cover 15-20 years, but the real service life can stretch 25-40 years if looked after properly. Guarantees focus on materials and workmanship, not wear and tear or how the roof’s used